Conventionally, a film made from a thermoplastic resin, such as polyolefin, polystyrene, poly(vinyl chloride), polyester, polyamide and the like, particularly an oriented film made from polypropylene, polyester, polyamide and the like have been widely used for their superior dynamic property, heat resistance, transparency and the like. In particular, a biaxially oriented polyester films are superior in mechanical strength, heat resistance, chemical resistance and dimensional stability, so that they have been used in a wide range of applications, such as a base film for magnetic tape, an insulating tape, a photographic film, a tracing film, a food packaging film and the like. On the other hand, since polyester films generally have poor adhesive property, it is a common practice to subject a polyester film to a corona discharge surface treatment or to form an anchor coating layer, when laminating thereon a layer of magnetic agent, photosensitive agent, mat agent and the like. As such anchor coating agent, a number of materials have been proposed, among which are water soluble or water dispersible polyester or acrylic resin to be used for a film having comparatively higher polarity, which is typically a polyester film (Japanese Patent Unexamined Publication Nos. 54-43017, Japanese Patent Examined Publication No. 49-10243 and U.S. Pat. No. 4,098,952).
The above-mentioned polyester resin is defective in that a film having an anchor coating layer made therefrom is susceptible to blocking when rolled, and the above-mentioned acrylic resin is defective in that an anchor coating layer therefrom sometimes shows insufficient adhesion to a layer to be formed thereon. In an attempt to overcome these drawbacks, it is proposed to use the above-mentioned polyester resin and acrylic resin in mixture (Japanese Patent Unexamined Publication No. 58-124651), though such method does not always satisfactorily compensate for the drawbacks.
It has been also proposed to use various modified polyesters typically represented by one modified by grafting. For example, Japanese Patent Unexamined Publication Nos. 2-3307, 2-171243 and 2-310048 teach that a resin obtained by grafting a compound having an unsaturated bond to a water soluble or water dispersible hydrophilic polyester resin is suitable as an anchor coating agent for a polyester film. Nevertheless, since in such a graft-modified resin, which has been made to have a hydrophilic group in advance in the polyester resin by, for example, copolymerization, the anchor coating layer therefrom is devoid of high adhesive property or water resistance. In such a case, addition of a crosslinking agent or an organic solvent is generally essential for complementing degraded properties.
In addition, Japanese Patent Unexamined Publication No. 3-273015 and U.S. Pat. No. 5,015,169 disclose that a graft-modified polyester resin is useful as an anchor-coating agent for a polyester film. While an anchor coating layer therefrom shows improved adhesive property in a dry state, the resin has poor cohesion, such that the adhesive property of the anchor coating layer under humidity becomes less and the film increasingly suffers from peeling off of a layer formed on the anchor coating layer, development of flaws and the like, as the number of process increases.
It is therefore an object of the present invention to resolve the above-mentioned problems and provide a thermoplastic laminate film having superior adhesion between a substrate film and an adhesion improving layer and between the adhesion improving layer and a layer formed thereon, superior resistance to water and solvent, superior slidability and superior transparency.
Accordingly, the present invention provides the following,
(1) A thermoplastic laminate film comprising a thermoplastic substrate film and a layer formed from a resin composition comprising a polyester graft copolymer (A) and a resin (B), the layer being formed on at least one side of the thermoplastic substrate film, the polyester graft copolymer (A) being obtained by grafting at least one polymerizable unsaturated monomer, which comprises an acid anhydride having a double bond, to a hydrophobic polyester resin, and the resin (B) comprising at least one member selected from the group consisting of a polyurethane resin, an acrylic resin and a vinyl resin.
(2) The thermoplastic laminate film of (1) above, wherein the resin (B) is a polyurethane resin, an acrylic resin or a vinyl resin.
(3) The thermoplastic laminate film of (1) above, wherein the resin (B) is a polyurethane resin or an acrylic resin.
(4) The thermoplastic laminate film of (1) above, wherein the resin (B) is a copolymer comprising at least two members selected from the group consisting of a polyurethane resin, an acrylic resin and a vinyl resin.
(5) The thermoplastic laminate film of (1) above, wherein the resin (B) is a copolymer comprising a polyurethane resin and an acrylic resin.
(6) The thermoplastic laminate film of (1) above, wherein the acid anhydride having a double bond is maleic anhydride.
(7) The thermoplastic laminate film of (1) above, wherein the polymerizable unsaturated monomer comprises at least maleic anhydride and styrene.
(8) The thermoplastic laminate film of (1) above, wherein the resin composition further comprises at least one member selected from the group consisting of a wax, an organic particle and an inorganic particle.
(9) The thermoplastic laminate film of (1) above, wherein the resin composition further comprises a static preventive.
(10) The thermoplastic laminate film of (1) above, wherein the resin composition further comprises a surfactant.
(11) The thermoplastic laminate film of (1) above, wherein the resin composition further comprises a crosslinking binder.
(12) The thermoplastic laminate film of (1) above, wherein the hydrophobic polyester resin in the polyester graft copolymer (A) comprises an aromatic dicarboxylic acid in 30-99.5 mol %, an aliphatic dicarboxylic acid and/or an alicyclic dicarboxylic acid in 0-70 mol % and a polymerizable unsaturated double bond-containing dicarboxylic acid in 0.5-10 mol %, as a dicarboxylic acid component.
(13) The thermoplastic laminate film of (1) above, wherein the hydrophobic polyester resin in the polyester graft copolymer (A) comprises an aromatic dicarboxylic acid in 60-99.5 mol %, an aliphatic dicarboxylic acid and/or an alicyclic dicarboxylic acid in 0-40 mol % and a polymerizable unsaturated double bond-containing dicarboxylic acid in 0.5-10 mol %, as a dicarboxylic acid component.
(14) The thermoplastic laminate film of (1) above, wherein the hydrophobic polyester resin in the polyester graft copolymer (A) comprises a hydrophilic group.
(15) The thermoplastic laminate film of (1) above, wherein the hydrophobic polyester resin in the polyester graft copolymer (A) comprises at least aliphatic dicarboxylic acid as a polymerizable component.
(16) The thermoplastic laminate film of (15) above, wherein the layer shows an absorbance ratio (X/Y) of not less than 0.05, the X being a peak absorbance of a carboxylic anhydride group of the acid anhydride in the layer and the Y being a peak absorbance of an ester group derived from the aliphatic dicarboxylic acid.
(17) The thermoplastic laminate film of (15) above, wherein the layer is devoid of adhesive property in a adhesive blocking test using chloroform.
(18) The thermoplastic laminate film of (1) above, obtained by the steps of:
(a) applying a coating solution on an unoriented or monoaxially oriented thermoplastic film, the coating solution comprising the polyester graft copolymer (A) and the resin (B) comprising at least one member selected from the group consisting of a polyurethane resin, an acrylic resin and a vinyl resin, PA1 (b) drying the film, PA1 (c) monoaxially or biaxially orienting the film, and PA1 (d) thermosetting the film.